This invention relates to rigid composite articles having a relatively thin, impression-retaining molded surface portion and a thick backing portion to support and reinforce the impression-retaining molded surface portion.
In the metal working art, patterns, models, mold cavities and duplicator models are required having hard rigid surfaces which accurately retain the molded dimensions and which will not bend, deflect or warp in use during machining and foundry operations such as mold preparation and machine duplication. In many instances the patterns and models are prepared by hand, or, where a multiplicity of the patterns or models is required, by replication of a master. Replication of the master is frequently accomplished by for example casting in bulk materials such as plaster. However, particularly where the article to be replicated is large, bulk casting materials undergo a large amount of shrinkage during curing, and consequently allowances for these large dimensional changes must be made in designing and making the master. Further, where the surface of the pattern is expected to undergo wear, as for example in duplicator models, plaster models have insufficient surface hardness to withstand repeated use without undue wear and loss of dimensional accuracy. Rigid thermoset resins having a high degree of surface hardness may be employed to overcome the problem of surface wear, however the cost of such materials particularly for making large parts may be prohibitive. Resin-fiberglass composites are also frequently employed in the pattern making art. These composites employ as the first, impression-retaining portion a gel-coat resin which is cast on the surface of the master, partially-cured to obtain a gelled or semiset surface layer, and then backed and reinforced by layers of fiberglass and resin. The completed composite structure must then be allowed to fully cure before use. A particular disadvantage of these latter systems lies in the necessity for obtaining a partial cure of the gel coat prior to adding the fiberglass-resin backing. Where the gel-coat is given no cure, the backing layers displace the gel-coat resin from the surface of the master, and where the gel coat is first permitted to completely cure before adding fiberglass layers, the backing layers adhere poorly if at all to the gel coat and provide inadequate reinforcement. The times required to cure first the gel coat and then the fiberglass-resin backing are relatively long, and the forming of models and patterns by these prior art methods is thus a slow and time-consuming process.